From: Alexander Potapenko <glider@google.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Dmitry Vyukov <dvyukov@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Marco Elver <elver@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Branislav Rankov <Branislav.Rankov@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
kasan-dev <kasan-dev@googlegroups.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH mm v10 41/42] kasan: add documentation for hardware tag-based mode
Date: Wed, 18 Nov 2020 16:43:16 +0100 [thread overview]
Message-ID: <CAG_fn=We3geXieMD1PzFGj+d6wj8_uEpkE=UOn=jfFEciQM2gQ@mail.gmail.com> (raw)
In-Reply-To: <f10443693b4dfd63477519e5f2e4fdc439c8c3c8.1605305705.git.andreyknvl@google.com>
On Fri, Nov 13, 2020 at 11:17 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> Add documentation for hardware tag-based KASAN mode and also add some
> clarifications for software tag-based mode.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
> ---
> Change-Id: Ib46cb444cfdee44054628940a82f5139e10d0258
> ---
> Documentation/dev-tools/kasan.rst | 80 +++++++++++++++++++++++--------
> 1 file changed, 59 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index 2d55d788971c..ffbae8ce5748 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -5,12 +5,14 @@ Overview
> --------
>
> KernelAddressSANitizer (KASAN) is a dynamic memory error detector designed to
> -find out-of-bound and use-after-free bugs. KASAN has two modes: generic KASAN
> -(similar to userspace ASan) and software tag-based KASAN (similar to userspace
> -HWASan).
> +find out-of-bound and use-after-free bugs. KASAN has three modes:
> +1. generic KASAN (similar to userspace ASan),
> +2. software tag-based KASAN (similar to userspace HWASan),
> +3. hardware tag-based KASAN (based on hardware memory tagging).
>
> -KASAN uses compile-time instrumentation to insert validity checks before every
> -memory access, and therefore requires a compiler version that supports that.
> +Software KASAN modes (1 and 2) use compile-time instrumentation to insert
> +validity checks before every memory access, and therefore require a compiler
> +version that supports that.
>
> Generic KASAN is supported in both GCC and Clang. With GCC it requires version
> 8.3.0 or later. Any supported Clang version is compatible, but detection of
> @@ -19,7 +21,7 @@ out-of-bounds accesses for global variables is only supported since Clang 11.
> Tag-based KASAN is only supported in Clang.
>
> Currently generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390
> -and riscv architectures, and tag-based KASAN is supported only for arm64.
> +and riscv architectures, and tag-based KASAN modes are supported only for arm64.
>
> Usage
> -----
> @@ -28,14 +30,16 @@ To enable KASAN configure kernel with::
>
> CONFIG_KASAN = y
>
> -and choose between CONFIG_KASAN_GENERIC (to enable generic KASAN) and
> -CONFIG_KASAN_SW_TAGS (to enable software tag-based KASAN).
> +and choose between CONFIG_KASAN_GENERIC (to enable generic KASAN),
> +CONFIG_KASAN_SW_TAGS (to enable software tag-based KASAN), and
> +CONFIG_KASAN_HW_TAGS (to enable hardware tag-based KASAN).
>
> -You also need to choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE.
> -Outline and inline are compiler instrumentation types. The former produces
> -smaller binary while the latter is 1.1 - 2 times faster.
> +For software modes, you also need to choose between CONFIG_KASAN_OUTLINE and
> +CONFIG_KASAN_INLINE. Outline and inline are compiler instrumentation types.
> +The former produces smaller binary while the latter is 1.1 - 2 times faster.
>
> -Both KASAN modes work with both SLUB and SLAB memory allocators.
> +Both software KASAN modes work with both SLUB and SLAB memory allocators,
> +hardware tag-based KASAN currently only support SLUB.
> For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
>
> To augment reports with last allocation and freeing stack of the physical page,
> @@ -196,17 +200,24 @@ and the second to last.
> Software tag-based KASAN
> ~~~~~~~~~~~~~~~~~~~~~~~~
>
> -Tag-based KASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to
> -store a pointer tag in the top byte of kernel pointers. Like generic KASAN it
> -uses shadow memory to store memory tags associated with each 16-byte memory
> +Software tag-based KASAN requires software memory tagging support in the form
> +of HWASan-like compiler instrumentation (see HWASan documentation for details).
> +
> +Software tag-based KASAN is currently only implemented for arm64 architecture.
> +
> +Software tag-based KASAN uses the Top Byte Ignore (TBI) feature of arm64 CPUs
> +to store a pointer tag in the top byte of kernel pointers. Like generic KASAN
> +it uses shadow memory to store memory tags associated with each 16-byte memory
> cell (therefore it dedicates 1/16th of the kernel memory for shadow memory).
>
> -On each memory allocation tag-based KASAN generates a random tag, tags the
> -allocated memory with this tag, and embeds this tag into the returned pointer.
> +On each memory allocation software tag-based KASAN generates a random tag, tags
> +the allocated memory with this tag, and embeds this tag into the returned
> +pointer.
> +
> Software tag-based KASAN uses compile-time instrumentation to insert checks
> before each memory access. These checks make sure that tag of the memory that
> is being accessed is equal to tag of the pointer that is used to access this
> -memory. In case of a tag mismatch tag-based KASAN prints a bug report.
> +memory. In case of a tag mismatch software tag-based KASAN prints a bug report.
>
> Software tag-based KASAN also has two instrumentation modes (outline, that
> emits callbacks to check memory accesses; and inline, that performs the shadow
> @@ -215,9 +226,36 @@ simply printed from the function that performs the access check. With inline
> instrumentation a brk instruction is emitted by the compiler, and a dedicated
> brk handler is used to print bug reports.
>
> -A potential expansion of this mode is a hardware tag-based mode, which would
> -use hardware memory tagging support instead of compiler instrumentation and
> -manual shadow memory manipulation.
> +Software tag-based KASAN uses 0xFF as a match-all pointer tag (accesses through
> +pointers with 0xFF pointer tag aren't checked). The value 0xFE is currently
> +reserved to tag freed memory regions.
> +
> +Software tag-based KASAN currently only supports tagging of
> +kmem_cache_alloc/kmalloc and page_alloc memory.
> +
> +Hardware tag-based KASAN
> +~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +Hardware tag-based KASAN is similar to the software mode in concept, but uses
> +hardware memory tagging support instead of compiler instrumentation and
> +shadow memory.
> +
> +Hardware tag-based KASAN is currently only implemented for arm64 architecture
> +and based on both arm64 Memory Tagging Extension (MTE) introduced in ARMv8.5
> +Instruction Set Architecture, and Top Byte Ignore (TBI).
> +
> +Special arm64 instructions are used to assign memory tags for each allocation.
> +Same tags are assigned to pointers to those allocations. On every memory
> +access, hardware makes sure that tag of the memory that is being accessed is
> +equal to tag of the pointer that is used to access this memory. In case of a
> +tag mismatch a fault is generated and a report is printed.
> +
> +Hardware tag-based KASAN uses 0xFF as a match-all pointer tag (accesses through
> +pointers with 0xFF pointer tag aren't checked). The value 0xFE is currently
> +reserved to tag freed memory regions.
> +
> +Hardware tag-based KASAN currently only supports tagging of
> +kmem_cache_alloc/kmalloc and page_alloc memory.
>
> What memory accesses are sanitised by KASAN?
> --------------------------------------------
> --
> 2.29.2.299.gdc1121823c-goog
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
next prev parent reply other threads:[~2020-11-18 15:43 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-13 22:15 [PATCH mm v10 00/42] kasan: add hardware tag-based mode for arm64 Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 01/42] kasan: drop unnecessary GPL text from comment headers Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 02/42] kasan: KASAN_VMALLOC depends on KASAN_GENERIC Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 03/42] kasan: group vmalloc code Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 04/42] kasan: shadow declarations only for software modes Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 05/42] kasan: rename (un)poison_shadow to (un)poison_range Andrey Konovalov
2020-11-18 15:30 ` Alexander Potapenko
2020-11-13 22:15 ` [PATCH mm v10 06/42] kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_* Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 07/42] kasan: only build init.c for software modes Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 08/42] kasan: split out shadow.c from common.c Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 09/42] kasan: define KASAN_MEMORY_PER_SHADOW_PAGE Andrey Konovalov
2020-11-18 15:36 ` Alexander Potapenko
2020-11-13 22:15 ` [PATCH mm v10 10/42] kasan: rename report and tags files Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 11/42] kasan: don't duplicate config dependencies Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 12/42] kasan: hide invalid free check implementation Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 13/42] kasan: decode stack frame only with KASAN_STACK_ENABLE Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 14/42] kasan, arm64: only init shadow for software modes Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 15/42] kasan, arm64: only use kasan_depth " Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 16/42] kasan, arm64: move initialization message Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 17/42] kasan, arm64: rename kasan_init_tags and mark as __init Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 18/42] kasan: rename addr_has_shadow to addr_has_metadata Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 19/42] kasan: rename print_shadow_for_address to print_memory_metadata Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 20/42] kasan: rename SHADOW layout macros to META Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 21/42] kasan: separate metadata_fetch_row for each mode Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 22/42] kasan, arm64: don't allow SW_TAGS with ARM64_MTE Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 23/42] kasan: introduce CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-11-18 16:04 ` Alexander Potapenko
2020-11-13 22:15 ` [PATCH mm v10 24/42] arm64: Enable armv8.5-a asm-arch option Andrey Konovalov
2020-11-18 15:48 ` Alexander Potapenko
2020-11-13 22:15 ` [PATCH mm v10 25/42] arm64: mte: Add in-kernel MTE helpers Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 26/42] arm64: mte: Reset the page tag in page->flags Andrey Konovalov
2020-11-14 12:43 ` Catalin Marinas
2020-11-13 22:15 ` [PATCH mm v10 27/42] arm64: mte: Add in-kernel tag fault handler Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 28/42] arm64: kasan: Allow enabling in-kernel MTE Andrey Konovalov
2020-11-14 12:47 ` Catalin Marinas
2020-11-13 22:15 ` [PATCH mm v10 29/42] arm64: mte: Convert gcr_user into an exclude mask Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 30/42] arm64: mte: Switch GCR_EL1 in kernel entry and exit Andrey Konovalov
2020-11-13 22:15 ` [PATCH mm v10 31/42] kasan, mm: untag page address in free_reserved_area Andrey Konovalov
2020-11-18 16:07 ` Alexander Potapenko
2020-11-13 22:16 ` [PATCH mm v10 32/42] arm64: kasan: Align allocations for HW_TAGS Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 33/42] arm64: kasan: Add arch layer for memory tagging helpers Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 34/42] kasan: define KASAN_GRANULE_SIZE for HW_TAGS Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 35/42] kasan, x86, s390: update undef CONFIG_KASAN Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 36/42] kasan, arm64: expand CONFIG_KASAN checks Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 37/42] kasan, arm64: implement HW_TAGS runtime Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 38/42] kasan, arm64: print report from tag fault handler Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 39/42] kasan, mm: reset tags when accessing metadata Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 40/42] kasan, arm64: enable CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-11-13 22:16 ` [PATCH mm v10 41/42] kasan: add documentation for hardware tag-based mode Andrey Konovalov
2020-11-18 15:43 ` Alexander Potapenko [this message]
2020-11-13 22:16 ` [PATCH mm v10 42/42] kselftest/arm64: Check GCR_EL1 after context switch Andrey Konovalov
2020-11-13 23:35 ` [PATCH mm v10 00/42] kasan: add hardware tag-based mode for arm64 Andrew Morton
2020-11-16 14:48 ` Vincenzo Frascino
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